1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which prevents the luminance from being varied when displaying moving images by inhibiting the delay of emission.
2. Description of Related Art
Generally, electron emission devices are classified into those using hot cathodes as an electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface conduction emitter (SCE) type.
The FEA type of electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the material due to the electric field in a vacuum atmosphere. A sharp-pointed tip structure based on molybdenum (Mo) or silicon (Si), or a carbonaceous material, such as carbon nanotube, graphite and diamond-like carbon, has been developed to be used as electron emission regions.
In common FEA type electron emission devices, cathode electrodes, an insulating layer and gate electrodes are sequentially formed on a first substrate, and openings are formed at the gate electrodes and the insulating layer. Electron emission regions are formed on the cathode electrodes within the openings. Phosphor layers and an anode electrode are formed on a surface of a second substrate facing the first substrate.
The cathode electrodes supply the electric current required for emitting electrons to the electron emission regions, and the gate electrodes control the electron emission using the voltage difference thereof from the cathode electrodes. The anode electrode receives a direct current (DC) voltage of several hundred to several thousand volts, and keeps the phosphor layers in a high potential state, thereby effectively accelerating the electrons emitted from the electron emission regions toward the phosphor layers.
Commonly, the gate electrodes are used as scan electrodes, and the cathode electrodes are used as data electrodes for carrying the image data.
Scan pulses are sequentially applied to the gate electrodes, and data pulses are selectively applied to the cathode electrodes corresponding to the gate electrodes receiving the scan pulses. Electric fields are formed around the electron emission regions at the pixels where the voltage difference between the two electrodes exceeds a threshold value, and electrons are emitted from the electron emission regions. The emitted electrons are attracted by the high voltage applied to the anode electrode, and collide against the corresponding phosphor layers, thereby light-emitting them.
With common electron emission devices, when the presence and the amount of electron emission are quickly and correctly controlled in accordance with the driving signals applied to the cathode and the gate electrodes, accurate displaying in accordance with image signals can be accomplished. The amount of electron emission is observed by the emission current reaching the anode electrode. The amount of electron emission and the emission current will hereinafter be used interchangeably.
The above problem can be exacerbated when the electron emission device displays moving images or the images are shifted while inducing considerably large-scaled variation in the emission current. For instance, when the images are shifted from the black mode to the white mode, the emission current should be quickly recovered in accordance with the driving signals. Otherwise, the luminance is deteriorated at the initial section of the white mode.
Rectangular wave pulses are typically applied to the cathode and the gate electrodes. The rectangular wave pulses involve relatively high voltages, and the larger the number of pixels involved, the shorter the application period of the ON time becomes. A signal distortion may result from a delay in the driving signals due to the parasitic capacitance generated at the crossed regions of the cathode and the gate electrodes, or from the internal resistance of the cathode and the gate electrodes. The delay of the driving signals results in an emission delay, and deteriorates the display quality.